Various electrophotographic developing systems for visualizing an electrostatic latent image formed on a carrier have been proposed according to the type of developers used. Among them is a transfer development system which uses a developer carrier called a donor as disclosed in U.S. Pat. No. 2,895,847. The terminology "transfer development" as used in the U.S. Patent includes (1) a system in which a photoreceptor and a toner layer (developer) are placed at a gap therebetween, and the toner flies over the gap, (2) a system in which a toner layer rotates in contact with a photoreceptor, and (3) a system in which a toner layer rotates in contact with a photoreceptor while sliding on the image area. Transfer development is well known as touch-down development.
Known one-component developing machines to be used for touch-down development include those for development with a one-component magnetic developer as disclosed, e.g., in JP-A-54-51848 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-U-58-146249 (the term "JP-A-U" as used herein means an "unexamined published Japanese utility model application"), and U.S. Pat. Nos. 3,372,675 and 3,426,730, whose schematic cross section is shown in FIG. 13, and those for development with a one-component non-magnetic developer as disclosed, e.g., JP-A-60-53975, whose schematic cross section is shown in FIG. 14.
The developing machine of FIG. 13 comprises hopper 33 for feeding one-component magnetic developer 34, cylindrical developer carrier 36 which is rotatably held by magnetic roll 35 having a plurality of magnetic poles, and developer controlling member 37. Electrostatic latent image carrier 31 (hereinafter referred to as a photoreceptor) facing to developer carrier 36 comprises an electrode having thereon a photoconductive layer, which is uniformly charged and then imagewise exposed to light to form electrostatic latent image 32. When one-component magnetic developer 34 contained in hopper 33 and supported on developer carrier 36 by the magnetic force of magnetic roll 35 passes between carrier 36 and developer controlling member 37, a film of the developer with a controlled thickness is formed, and a necessary quantity of charge is given thereto.
Developer controlling member 37 includes a member which or at least the surface of which is made of an elastic material, e.g., rubber, as shown in FIG. 13 and a magnetic or non-magnetic plate which is held to face developer carrier 36 at a given gap. Developer 34 in film form is forwarded to developing zone A where photoreceptor 31 and developer carrier 36 face to each other. A D.C./A.C. superimposed current voltage (hereinafter referred to as a superimposed current) from high-voltage A.C. power supply 38 and D.C. power supply 39 is applied to developer carrier 36, and charged developer 34 on developer carrier 36 flies to electrostatic latent image 32 on photoreceptor 31 through the oscillation electric field generated in developing zone A to thereby visualize the latent image.
The developing machine shown in FIG. 14 comprises hopper 43 containing non-magnetic one-component developer 44, developer carrier 46, developer supply roll 50 which rotates at the same peripheral speed as that of developer carrier 46 in the opposite direction, and developer controlling member 47 contacting developer carrier 46 under a prescribed contact pressure. Developer 44 supplied to developer carrier 46 by supply roll 50 is carried to developer controlling member 47 by the revolution of carrier 46, where a film of the developer with a controlled thickness is formed, and a necessary quantity of charge is given thereto. Developer 44 in film form is forwarded to developing zone A where photoreceptor 41 and developer carrier 46 face each other. A superimposed current voltage from high-voltage A.C. power supply 48 and D.C. power supply 49 is applied to developer carrier 46, and charged developer 44 on developer carrier 46 flies to electrostatic latent image 42 on photoreceptor 41 through the oscillation electric field generated in developing zone A to thereby visualize the latent image.
Developer carrier 36 or 46 in these types of developing machines is a sleeve made of aluminum or stainless steel coated with a semiconductive material, such as high-molecular weight resin, e.g., a phenolic resin or an epoxy resin, having dispersed therein a resistivity controlling agent and a reinforcement. The surface of the sleeve may be mechanically abraded by emery, etc. to have a prescribed surface roughness. A sleeve made of a semiconductive resin with its inner wall rendered conductive by coating a conducting agent, etc. and with its outer surface mechanically abraded may also be used as a developer carrier.
As developer 34 or 44 passes between developer controlling member 37 or 47 and developer carrier 36 or 46, it forms a thin layer and, at the same time, is given positive or negative electric charges according to the charging polarity of developer 34 or 44 by triboelectricity. Developer 34 or 44 is carried on the uneven surface of developer carrier 36 or 46. If the surface roughness (Rz) of developer carrier 36 or 46 is less than 0.5 .mu.m, the amount of developer 34 or 44 carried is insufficient for obtaining a satisfactory image density. If Rz is 10 .mu.m or greater, the excess of developer 34 or 44 carried has no contact with developer carrier 36 or 46, resulting in a failure of causing sufficient triboelectricity. Accordingly, developer carrier 36 or 46 preferably has a surface roughness Rz of from 0.5 to 10 .mu.m.
Magnetic one-component developer 34 may be replaced with a non-magnetic one-component developer. In this case, magnetic roll 35 in developer carrier 36 is unnecessary.
In order to charge one-component developer by triboelectricity, it is effective to incorporate a triboelectricity-imparting agent into developer carrier 36 or 46. A number of triboelectricity-imparting agents to be incorporated into developer carrier 36 or 46 have been proposed to date, including metal oxide particles (JP-A-1-142563), a reaction product of a di-organotin oxide and boric acid or an organoboric acid (JP-A-63-5352), a bis(di-organotin carboxylic acid)dicarboxylic acid salt (JP-A-63-5353), a tri-organotin carboxylic acid (JP-A-63-5355), a triazine condensation product (JP-A-63-5356), a compound represented by formula R.sub.1 NHR.sub.2 NHCNR.sub.3 (JP-A-63-5357), a di-organotin borate (JP-A-63-5358), a di-organotin phosphate (JP-A-63-5359), a polymer of a monomer represented by formula CH.sub.2 CRXPR.sub.2 R.sub.3 or a copolymer of the monomer and a vinyl monomer (JP-A-63-157168), a triphenylmethane compound (JP-A-63-159866), a compound represented by formula R.sub.1 R.sub.2 P(CH.sub.2).sub.n PR.sub.3 R.sub.4 (JP-A-63-159867), metal oxide particles (JP-A-1-142562), and a silicone resin containing an aminosilane coupling agent (JP-A-1-147478).
Some of these triboelectricity-imparting agents which can be dispersed in a developer carrier achieves effects to some extent but not to a sufficient extent.